Transmitting device, receiving device, communication device, programs, transmission method, and receiving method for wireless communication of continuous data in the form of packets

ABSTRACT

Transmitting device, receiving device, communication device, programs, transmission method, and receiving method for wireless communication of continuous data in the form of packets. A transmitting device includes a data receiving unit that receives continuous data from a network, the continuous data including actual data and null data; a packetizing unit that deletes at least a part of the null data from the continuous data to generate a packet for wireless communication; a transmitting unit that modulates the packet into a radio carrier wave and wirelessly transmits the resulting packet; and a control unit that causes the transmitting unit to stop transmission of the radio carrier wave during at least a part of a time period in which no such packet is transmitted wirelessly.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §371 from PCTApplication PCT/JP2014/060524, filed on Apr. 11, 2014, which claimspriority from Japanese Patent Application No. 2013-094907, filed Apr.30, 2013. The entire contents of both applications are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a transmitting device, a receivingdevice, a communication device, programs, a transmission method, and areceiving method for wireless communication of continuous data in theform of packets.

BACKGROUND

There is known a transmitting device which deletes a part of null datafrom continuous data on a network such as the Ethernet (registeredtrademark) and transmits the continuous data including actual data (see,for example, Japanese Patent Application Publication No. 2009-141841).

SUMMARY OF THE INVENTION

With the above-described technique, however, a large amount of powerwould be consumed by a radio carrier wave.

A first aspect of the present invention provides a transmitting devicewhich includes: a data receiving unit that receives continuous data froma network, the continuous data including actual data and null data; apacketizing unit that deletes at least a part of the null data from thecontinuous data to generate a packet for wireless communication; atransmitting unit that modulates the packet into a radio carrier waveand wirelessly transmits the resulting packet; and a control unit thatcauses the transmitting unit to stop transmission of the radio carrierwave during at least a part of a time period in which no such packet istransmitted wirelessly.

A second aspect of the present invention provides a receiving devicewhich includes: a receiving unit that demodulates a radio carrier wavetransmitted wirelessly from a transmitting side into a packet andreceives the resulting packet, the radio carrier wave being transmittedin the state where at least a part of null data has been deleted on thetransmitting side from continuous data received from a first network,the continuous data including actual data and the null data; a datagenerating unit that adds the null data to, or deletes the null datafrom, the packet to generate continuous data; and a data transmittingunit that transmits the continuous data including the actual data andthe null data to a second network.

A third aspect of the present invention provides a communication devicewhich includes the transmitting device and the receiving devicedescribed above.

A fourth aspect of the present invention provides a program fortransmission for causing a computer to function as: a data receivingunit that receives continuous data from a network, the continuous dataincluding actual data and null data; a packetizing unit that deletes atleast a part of the null data from the continuous data to generate apacket for wireless communication; a transmitting unit that modulatesthe packet into a radio carrier wave and wirelessly transmits theresulting packet; and a control unit that causes the transmitting unitto stop transmission of the radio carrier wave during at least a part ofa time period in which no such packet is transmitted wirelessly.

A fifth aspect of the present invention provides a program for receptionfor causing a computer to function as: a receiving unit that demodulatesa radio carrier wave transmitted wirelessly from a transmitting sideinto a packet and receives the resulting packet, the radio carrier wavebeing transmitted in the state where at least a part of null data hasbeen deleted on the transmitting side from continuous data received froma first network, the continuous data including actual data and the nulldata; a data generating unit that adds the null data to, or deletes thenull data from, the packet to generate continuous data; and a datatransmitting unit that transmits the continuous data including theactual data and the null data to a second network.

A sixth aspect of the present invention provides a transmission methodwhich includes: a data receiving step of receiving continuous data froma network, the continuous data including actual data and null data; apacketizing step of deleting at least a part of the null data from thecontinuous data to generate a packet for wireless communication; atransmitting step of modulating the packet into a radio carrier wave andwirelessly transmitting the resulting packet; and a control step ofcausing transmission of the radio carrier wave in the transmitting stepto be stopped during at least a part of a time period in which no suchpacket is transmitted wirelessly.

A seventh aspect of the present invention provides a receiving methodwhich includes: a receiving step of demodulating a radio carrier wavetransmitted wirelessly from a transmitting side into a packet andreceiving the resulting packet, the radio carrier wave being transmittedin the state where at least a part of null data has been deleted on thetransmitting side from continuous data received from a first network,the continuous data including actual data and the null data; a datagenerating step of adding the null data to, or deleting the null datafrom, the packet to generate continuous data; and a data transmittingstep of transmitting the continuous data including the actual data andthe null data to a second network.

The summary of the invention described above does not list all thefeatures indispensable to the present invention; any sub-combination ofthese features can also embody the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the overall configuration of a communication system 10;

FIG. 2 illustrates changes of data as it is transmitted from atransmitting-side Ethernet to a receiving-side Ethernet;

FIG. 3 illustrates changes of data as it is transmitted from atransmitting-side Ethernet to a receiving-side Ethernet;

FIG. 4 illustrates a data structure of a packet WP;

FIG. 5 illustrates another data structure of a packet WP;

FIG. 6 is a flowchart illustrating a process of writing a fixed-lengthpacket WP to a storage unit 18, performed by a packetizing unit 22 in atransmitting device 14;

FIG. 7 is a flowchart illustrating a process of reading a fixed-lengthpacket WP from the storage unit 18, performed by the packetizing unit 22in the transmitting device 14;

FIG. 8 is a flowchart illustrating a process of writing a receivedfixed-length packet WP to a storage unit 18, performed by a datagenerating unit 32 in a receiving device 16;

FIG. 9 is a flowchart illustrating a process of reading a fixed-lengthpacket WP which has been written into the storage unit 18, performed bythe data generating unit 32 in the receiving device 16;

FIG. 10 is a graph showing the relationship between the percentage ofnull data IFS and the percentage of reduction in output;

FIG. 11 is a graph showing the relationship between the size of thepacket WP and the percentage of reduction in output;

FIG. 12 is a graph showing the relationship between the size of thepacket WP and the latency; and

FIG. 13 shows an exemplary hardware configuration of a computer 1900according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention will be described below with reference to anembodiment, the following embodiment is not to restrict the inventionrecited in the claims for patent. Further, all the combinations of thefeatures discussed in the embodiment are not necessarily indispensablefor the solving means of the invention.

FIG. 1 shows the overall configuration of a communication system 10. Thecommunication system 10 includes a plurality of communication devices12. In the example shown in FIG. 1, the communication system 10 includestwo communication devices 12. Each communication device 12 has atransmitting device 14, a receiving device 16, and a storage unit 18. Ina communication device 12, the transmitting device 14 modulates a packetWP, having at least a part of null data IFS deleted from continuous dataSD input from a wired transmitting-side Ethernet, into a radio carrierwave and transmits the resulting packet. Here, the transmitting device14 makes the amplitude of the radio carrier wave zero during at least apart of the time period in which no packet WP is wirelessly transmitted,so as to stop the transmission of the radio carrier wave. This canreduce the power consumed in the communication device 12. The receivingdevice 16 generates continuous data from a received packet WP, and addsnull data to, or deletes null data from, the continuous data beforetransmitting it to a wired receiving-side Ethernet. The Ethernet is anexample of a network. The Ethernet has a communication speed of, forexample, 10 Mbps, 100 Mbps, 1 Gbps, or 10 Gbps. The Ethernet offers, forexample, a full-duplex communication system, although it can offeranother communication system. Further, the Ethernet can conform tofuture standards.

The transmitting device 14 has a data receiving unit 20, a packetizingunit 22, a control unit 24, and a transmitting unit 26. The datareceiving unit 20 is connected to the wired transmitting-side Ethernet.The data receiving unit 20 receives continuous data SD from anotherapparatus on the transmitting-side Ethernet. The continuous data SDincludes actual data PC, including images, characters, and otherinformation, and also includes null data IFS. The data receiving unit 20is, for example, a circuit in conformity to the media independentinterface (MII) standard defined in the Ethernet. It is noted that MIIincludes GMII, XMII, and RGMII.

The packetizing unit 22 is connected to the data receiving unit 20. Thepacketizing unit 22 acquires the continuous data SD, including actualdata PC and null data IFS, from the data receiving unit 20. Thepacketizing unit 22 deletes at least a part of the null data IFS. Forexample, when there is continuous null data IFS of a predeterminedlength or longer, the packetizing unit 22 deletes the null data IFS ofthe predetermined length or longer. The predetermined length here is 96bits, which is the minimum length of null data IFS between the pieces ofactual data PC, defined in the Ethernet. The packetizing unit 22generates a packet WP to be transmitted by a radio carrier wave, andoutputs the packet to the transmitting unit 26. For example, thepacketizing unit 22 generates a fixed-length packet WP whose data amountis predetermined, by deleting the null data IFS. Alternatively, thepacketizing unit 22 can generate a variable-length packet WP whose dataamount can vary, by deleting the null data IFS.

The transmitting unit 26 is connected to the packetizing unit 22. Thetransmitting unit 26 acquires the packet WP from the packetizing unit22. The transmitting unit 26 modulates the packet WP, with at least apart of null data IFS deleted from the continuous data SD, into a radiocarrier wave and transmits the resulting packet wirelessly.

The control unit 24 is connected to the data receiving unit 20, thepacketizing unit 22, and the transmitting unit 26, and controls the datareceiving unit 20 and the transmitting unit 26. For example, the controlunit 24 acquires, from the packetizing unit 22, information about theexistence of a packet WP to be transmitted, and stops the transmissionof the radio carrier wave by the transmitting unit 26 during at least apart of the time period in which no packet WP is transmitted wirelessly.It is noted that the control unit 24 can cause the transmitting unit 26to stop the transmission of the radio carrier wave, independently of thepacketizing unit 22. For example, the control unit 24 can cause thetransmitting unit 26 to stop the transmission of the radio carrier wavewhen the control unit 24 acquires information to the effect that thereis no actual data PC received from the data receiving unit 20. Thecontrol unit 24 also stops the transmission of the radio carrier wavewhen the time period in which null data IFS is transmitted wirelesslyhas continued for a predetermined length or longer.

The receiving device 16 has a receiving unit 30, a data generating unit32, and a data transmitting unit 34. The receiving unit 30 demodulatesthe radio carrier wave that the transmitting side has wirelesslytransmitted, with at least a part of null data IFS deleted from thecontinuous data SD including actual data PC and null data IFS that wasreceived from the transmitting-side Ethernet, and receives the packetWP. The receiving unit 30 outputs the packet WP to the data generatingunit 32.

The data generating unit 32 is connected to the receiving unit 30. Thedata generating unit 32 acquires the packet WP from the receiving unit30. The data generating unit 32 adds null data IFS to, or deletes nulldata IFS from, the packet WP to generate continuous data SD. Forexample, in the case where the transmitting side has deleted null dataIFS and, thus, the spacing between the pieces of actual data PC is lessthan a predetermined length, the data generating unit 32 adds null dataIFS so as to make the spacing between the pieces of actual data PC notless than the predetermined length. The predetermined length of spacinghere is, by way of example, 96 bits, which is defined in the Ethernet.Further, the data generating unit 32 adds null data IFS to thecontinuous data SD during the time period in which no radio carrier waveis received. Here, it is preferable that the data generating unit 32adds or deletes null data IFS in accordance with the amount ofunprocessed data in the packet WP transmitted from the transmittingside. This enables the receiving device 16 on the receiving side to workwith no problems even if the receiving device 16 on the receiving sidehas lower processing capacity than the transmitting device 14 on thetransmitting side.

The data transmitting unit 34 is connected to the data generating unit32. The data transmitting unit 34 acquires the continuous data SD fromthe data generating unit 32. The data transmitting unit 34 is connectedto a wired receiving-side Ethernet. The data transmitting unit 34transmits the continuous data SD, including actual data PC and null dataIFS, to another apparatus on the receiving-side Ethernet. The datatransmitting unit 34 is, for example, a circuit in conformity to MIIdefined in the Ethernet.

The storage unit 18 is connected to the transmitting device 14 and thereceiving device 16. The storage unit 18 temporarily buffers a packet WPbefore transmission in the transmitting device 14 and a packet WPreceived in the receiving device 16. Specifically, the storage unit 18stores the packet WP to be transmitted, which is input from thepacketizing unit 22. The storage unit 18 outputs the packet WP to betransmitted, stored therein, to the packetizing unit 22. The storageunit 18 stores the packet WP received, which is input from the datagenerating unit 32. The storage unit 18 outputs the packet WP receivedand stored, to the data generating unit 32. The storage unit 18 is, forexample, a first-in/first-out (FIFO) memory.

FIG. 2 illustrates changes of data as it is transmitted from atransmitting-side Ethernet to a receiving-side Ethernet. FIG. 2 showsthe case of transmitting/receiving a packet WP with all null data IFSdeleted. In FIG. 2, the horizontal axis represents time.

On the transmitting device 14 side, firstly, the transmitting-sideEthernet inputs continuous data SD, shown at the top in FIG. 2, to thedata receiving unit 20. The continuous data SD includes actual data PCand null data IFS that fills between the pieces of actual data PC.

As shown in the second and third rows from the top in FIG. 2, the datareceiving unit 20 outputs the Ethernet actual data PC, included in thecontinuous data SD transferred in the form of 10-bit MII code, to thepacketizing unit 22.

The packetizing unit 22 extracts the actual data PC from the continuousdata SD input from the data receiving unit 20, by using a two-bitcontrol signal included in the 10-bit MII code, without decoding the MIIdata signal. The packetizing unit 22 causes the storage unit 18 totemporarily store the data from which all null data IFS that does nothave to be transferred has been deleted, as a packet WP. Here, it ispreferable that the packetizing unit 22 causes the transmitting unit 26to transmit the packet WP only after the continuous data SD transmittedfrom the transmitting-side Ethernet via the data receiving unit 20 hasbeen processed by a predetermined minimum data amount ML or more and theprocessed data has been stored into the storage unit 18. This allows thetransmitting unit 26 to start transmission after the predeterminedminimum data amount ML or more of the continuous data SD has beenprocessed and stored into the storage unit 18. Preferably, the minimumdata amount ML is determined to satisfy the following expression, inconsideration of the time during which transmission of the radio carrierwave is stopped. As the minimum data amount ML increases, the outputtime of the radio carrier wave decreases, and the latency increases. Itis still more preferable that the packetizing unit 22 causes thetransmitting unit 26 to transmit the packet WP after the minimum dataamount ML of the MII codes has been processed and when the currentlyprocessed piece of Ethernet actual data PC has been processed to itstail end.ML*T _(Ethernet clock)>(ML+WO)*T _(wireless clock)

-   -   T_(Ethernet clock)>T_(wireless clock)    -   ML: minimum data processing amount    -   T_(Ethernet clock): Ethernet clock cycle    -   T_(wireless clock): Wireless clock cycle    -   WO: Wireless overhead

As shown in the fourth row from the top in FIG. 2, the packetizing unit22 causes the transmitting unit 26 to modulate the packet WP, which hasbeen obtained by deleting the null data IFS and stored in the storageunit 18, into a radio carrier wave and transmit the resulting packet.Here, the control unit 24 stops the radio carrier wave during the timebetween one packet WP and another packet WP, which is created as thenull data IFS is deleted. That is, the control unit 24 stops thetransmission of the radio carrier wave during the time period in whichno Ethernet actual data PC is transmitted.

On the receiving side, the receiving unit 30 receives the radio carrierwave shown in the fourth row from the top in FIG. 2. The receiving unit30 outputs the received packet WP to the data generating unit 32. Asshown in the fifth and sixth rows from the top in FIG. 2, the datagenerating unit 32 adds null data IFS to reconstruct the continuous dataSD in the MII codes from the received packet WP. For example, the datagenerating unit 32 adds null data IFS such that the spacing between thepieces of Ethernet actual data PC becomes 96 bits, which is the Ethernetstandard. Further, the data generating unit 32 can add or delete nulldata IFS so as to resolve the asynchronism which is attributable to thedifference in standards (for example, TX and RX) and to the errorbetween the self clock and the clock of the transmitting device 14 thathas transmitted the radio carrier wave. It is noted that the datagenerating unit 32 can perform flow control, insertion of “Carrierextend”, or other operations, as necessary, in accordance with theEthernet standards such as carrier sense multiple access/collisiondetection (CSMA/CD). The data generating unit 32 reconstructs thecontinuous data SD including actual data PC and null data IFS, shown inthe seventh row from the top in FIG. 2, and temporarily stores the datainto the storage unit 18. The data transmitting unit 34 reads thecontinuous data SD from the storage unit 18, and outputs the read datato the receiving-side Ethernet.

FIG. 3 illustrates changes of data as it is transmitted from atransmitting-side Ethernet to a receiving-side Ethernet. FIG. 3 showsthe case of transmitting/receiving a fixed-length packet WP with atleast a part of null data IFS deleted. In FIG. 3, the horizontal axisrepresents time. On the transmitting side, the transmitting-sideEthernet inputs continuous data SD, shown at the top in FIG. 3, to thedata receiving unit 20. The data receiving unit 20 outputs thecontinuous data SD to the packetizing unit 22.

As shown in the fourth row from the top in FIG. 3, the packetizing unit22 extracts actual data PC from the continuous data SD input from thedata receiving unit 20, and generates data with at least a part of nulldata IFS deleted, as a packet WP. The packetizing unit 22 stores thegenerated packet into the storage unit 18. Here, it is preferable forthe packetizing unit 22 to delete the null data IFS such that the nulldata IFS will not be at the top of the packet WP. This can lengthen thetime during which the transmitting unit 26 can stop the radio carrierwave, so that the power consumption can further be reduced.

The packetizing unit 22 deletes a part of the null data IFS so as tomake the packet WP have a predetermined fixed length. In the case ofgenerating a fixed-length packet WP, it is further preferable for thepacketizing unit 22 to generate a packet WP that maintains the temporalrelationship between the pieces of Ethernet actual data PC, withoutdeleting the null data IFS present between the pieces of Ethernet actualdata PC included in one packet WP.

The packetizing unit 22 reads the packet WP stored in the storage unit18, and causes the transmitting unit 26 to transmit the packet in thestate where it is modulated into a radio carrier wave. Here, thetransmitting unit 26 transmits the fixed-length packet WP whilemaintaining the Ethernet timing, i.e. the MII code timing. It is notedthat, on the transmitting side, the latency from when the data receivingunit 20 starts receiving actual data PC in continuous data SD until whenthe transmitting unit 26 starts transmitting the data at the head of apacket WP is substantially the same for all packets WP. Here, wirelessdata transfer is faster than wired data transfer. The control unit 24can therefore cause the transmitting unit 26 to stop transmission of theradio carrier wave during the time between a preceding packet WP and asucceeding packet WP which is created due to the above-describeddifference in frequency between wireless clock and wired clock and dueto the deletion of null data IFS. Further, when the null data IFScontinuing for a predetermined time or longer causes a packet WP toattain a fixed length or longer, the control unit 24 causes thetransmitting unit 26 to stop the transmission of the radio carrier waveby refraining from transmitting the null data IFS. Here, in the case ofa packet WP that maintains the temporal relationship between the piecesof Ethernet actual data PC, the transmitting unit 26 can wirelesslytransmit the packet while maintaining the MII data timing of thecontinuous data SD. This allows the data generating unit 32 in thereceiving device 16 to reconstruct the continuous data SD at the timingsubstantially the same as that on the transmitting side. It is thuspossible to decrease the uncertainty in the receiving time of the packetWP, thereby enabling transmission with reduced latency. Accordingly, itis possible to secure a proper order between the time when the lastpiece of data in a preceding packet WP is transmitted to the wiredEthernet on the data transmitting unit 34 and the time when a nextpacket WP is received on the receiving unit 30. This ensures that, onthe receiving side, the data transmitting unit 34 transmits the lastpiece of data in a preceding packet WP to the wired Ethernet after thereceiving unit 30 has received a succeeding packet WP, therebyeliminating data shortage.

On the receiving device 16 side, the receiving unit 30 receives theradio carrier wave shown in the fourth row from the top in FIG. 3. Onthe receiving side, once the first part of each packet WP is received,the receiving unit 30 transmits the data immediately to a wiredEthernet, without storing the data. On the receiving side, the latencyfrom when the first part of data in a packet WP is received until whenit is transferred to the wired Ethernet is substantially the same forall packets WP. That is, on the receiving side, a packet WP istransmitted to the wired Ethernet immediately upon arrival of thepayload of the packet WP. The receiving unit 30 outputs the packet WP,demodulated from the received radio carrier wave, to the data generatingunit 32. As shown in the fifth and sixth rows from the top in FIG. 3,the data generating unit 32 adds null data IFS on the basis of theEthernet clock on the receiving side, which is different from that onthe transmitting side, to thereby reconstruct the continuous data SDincluding Ethernet actual data PC from the received packet WP. The datagenerating unit 32 temporarily stores the resulting data into thestorage unit 18. In this manner, the data generating unit 32 causes thedata between the pieces of Ethernet actual data PC reconstructed, tocomply with the Ethernet standard. Here, in the case where the Ethernetactual data PC continues for a long time and null data IFS cannot bedeleted in the transmitting device 14, it is preferable for the datagenerating unit 32 to delete a part of the null data IFS in thereconstructed continuous data SD, or add null data IFS to the continuousdata SD, for clock timing adjustment, so as to resolve the asynchronismbetween the Ethernet clocks on the transmitting side and the receivingside. Further, the data generating unit 32 adds null data IFS during thetime period in which no radio carrier wave is received. The datagenerating unit 32 reads the reconstructed continuous data SD from thestorage unit 18 and outputs the read data to the data transmitting unit34. The data transmitting unit 34 outputs the continuous data SDincluding the actual data PC and the null data IFS, shown in the seventhrow from the top in FIG. 3, to the receiving-side Ethernet. Here, in thecase where the actual data PC in the continuous data SD has been dividedinto two packets WP on the transmitting side, the receiving unit 30receives the first part of the payload of a second packet WP at the timewhen the data transmitting unit 34 transmits the last part of thefirstly received packet WP to the wired Ethernet. Accordingly, on thereceiving side, the data generating unit 32 can readily reconstruct theactual data PC of the continuous data SD that was divided into the firstpacket WP and the second packet WP.

FIG. 4 illustrates a data structure of a packet WP. As an example, thepacket WP shown in FIG. 4 is a variable-length packet with all null dataIFS deleted. The packet WP shown in FIG. 4 includes a packet lengthW_Length, a packet length E_Length, and Ethernet actual data PC. Thepacket length W_Length is information indicating the entire length ofthe packet WP. The packet length E_Length is information indicating thelength of the actual data PC in the Ethernet continuous data SD includedin the packet WP. The packet length is calculated by counting the MIIcodes. As such, even in the case where the packetizing unit 22 in thetransmitting device 14 on the transmitting side has deleted all nulldata IFS in the continuous data SD, the packet length E_Length isincluded in the packet WP. This enables the receiving device 16 on thereceiving side to divide a plurality of pieces of Ethernet actual dataPC included in the received packet(s) WP, in accordance with the packetlength E_Length, to thereby reconstruct the actual data PC in theoriginal state. In the example shown in FIG. 4, the Ethernet actual dataPC is included in a single packet WP, without being divided into pieces.It is noted that a packet WP can include “Padding Length” whichindicates the length of null data IFS added for the purpose of adjustingthe length of the packet WP.

FIG. 5 illustrates another data structure of a packet WP. As an example,the packet WP shown in FIG. 5 is a variable-length packet with a part ofnull data IFS deleted. The packet WP shown in FIG. 5 includes a packetlength W_Length of the packet WP, and a plurality of pieces of normaldata. The normal data includes, for example, 8-bit data “Data” and a1-bit or 2-bit control signal CS. For example, when the control signalCS is “N”, it means that the 8-bit data “Data” is actual data PCincluded in the continuous data SD. When the control signal CS is “I”,it means that the 8-bit data “Data” is null data IFS included in thecontinuous data SD. As such, the packetizing unit 22 in the transmittingdevice 14 on the transmitting side has left a part of null data IFS inthe continuous data SD. This enables the receiving device 16 on thereceiving side to detect the null data IFS included in the receivedpacket WP as a boundary between the pieces of actual data PC in thecontinuous data SD, and divide and reconstruct the pieces of Ethernetactual data PC to the original state. In the example shown in FIG. 5,the Ethernet actual data PC can be divided to belong to two packets WP.

FIG. 6 is a flowchart illustrating a process of writing a fixed-lengthpacket WP to the storage unit 18, performed by the packetizing unit 22in the transmitting device 14. As shown in FIG. 6, in the writingprocess in the transmitting device 14, when continuous data SD is inputfrom the transmitting-side Ethernet, the packetizing unit 22 determineswhether the data is actual data PC or null data IFS in the Ethernetcontinuous data SD, on the basis of the MII code (S100). If thepacketizing unit 22 determines that the input continuous data SD is theactual data PC (Yes in S100), the packetizing unit 22 determines whethera write count WC, indicating the count of data written into the storageunit 18, is zero (S102).

If the packetizing unit 22 determines that the write count WC is 0 (Yesin S102), it means that nothing has been written in a next packet WP,and therefore, the packetizing unit 22 writes a fixed-length packetheader into the head of the packet WP (S106). On the other hand, if thepacketizing unit 22 determines that the write count WC is not 0 (No inS102), it means that a header and actual data PC have already beenwritten into a part of the packet WP, and therefore, the packetizingunit 22 refrains from writing a header. Thereafter, the packetizing unit22 writes the acquired Ethernet actual data PC, as data, into thestorage unit 18, to add the data to the packet WP (S108).

Next, the packetizing unit 22 determines whether the write count WC isequal to a packet length WL indicating the length of the fixed-lengthpacket WP (S110). If the packetizing unit 22 determines that the writecount WC is equal to the packet length WL (Yes in S110), it means thatone packet WP has been completed, and therefore, the packetizing unit 22initializes the data flag and the write count WC (S112). On the otherhand, if the packetizing unit 22 determines that the write count WC isnot equal to the packet length WL (No in S110), it means that the packetWP is being generated, and therefore, the packetizing unit 22 does notperform initialization. Thereafter, the packetizing unit 22 repeats stepS100 and subsequent steps.

After the packetizing unit 22 has determined in step S100 that the inputcontinuous data SD is null data IFS (No in S100), if the packetizingunit 22 determines that the immediately preceding continuous data SD wasactual data PC (Yes in S114), the packetizing unit 22 proceeds to stepS102 and performs step S102 and subsequent steps. In this case, in stepS108, the packetizing unit 22 writes the null data IFS, as data, intothe storage unit 18. When the tail end of the fixed-length packet WPcoincides with the tail end of the Ethernet actual data PC, thepacketizing unit 22 adds null data IFS following the tail end of thepacket WP. As a result, even in the case where the tail end of thepreceding packet WP is not null data IFS but coincides with the tail endof the Ethernet actual data PC, the null data IFS is transmitted in thesucceeding packet WP, following the transmission of the preceding packetWP. This allows the receiving device 16 to determine that the precedingpacket WP has ended with the tail end of the Ethernet actual data PC.

On the other hand, if the packetizing unit 22 determines that theimmediately preceding data was not the actual data PC (No in S114) butthe null data IFS, the packetizing unit 22 determines whether the datawhich has been written as the packet WP includes any Ethernet data thatshould be transmitted, or in other words, whether the data written inthe storage unit 18 includes only null data IFS that can be deleted(S116). The packetizing unit 22 can use a flag indicating the presenceor absence of actual data PC to determine the existence of the actualdata PC. If the packetizing unit 22 determines that the packet WPincludes actual data PC (Yes in S116), the packetizing unit 22 writesthe input null data IFS into the storage unit 18 (S118), and thenperforms step S110 and subsequent steps. On the other hand, if thepacketizing unit 22 determines that the packet WP does not include anyactual data PC (No in S116), the packetizing unit 22 deletes the inputnull data IFS without writing it (S120), and then performs step S100 andsubsequent steps. In other words, the packetizing unit 22 determineswhether to truncate or write the received null data IFS, in step S116,depending on whether the packet WP includes only null data IFS or not.At this time, the above-described null data IFS which is to be addedwhen the tail end of the fixed-length packet WP coincides with the tailend of the Ethernet actual data PC is treated in the same way as theEthernet actual data PC.

FIG. 7 is a flowchart illustrating a process of reading a fixed-lengthpacket WP from the storage unit 18, performed by the packetizing unit 22in the transmitting device 14. As shown in FIG. 7, in the readingprocess in the transmitting device 14, the packetizing unit 22determines whether the number #1 of pieces of data stored in the storageunit 18 is greater than a threshold value Th (S200). The number #1 ofpieces of data is a value that increases or decreases in accordance withthe writing or reading process. The threshold value Th, which is usedfor schedule management of wireless transmission, is set on the basis ofthe fixed length WL of the packet WP. The packetizing unit 22 repeatsstep S200 (No in S200) until the packetizing unit 22 determines that thenumber #1 of pieces of data is greater than the threshold value Th.

In the case where the packetizing unit 22 determines that the number ofpieces of data is greater than the threshold value Th (Yes in S200), itdetermines whether the number #1 of pieces of data is 0 (S202). In thecase where step S202 is performed after step S200, the number #1 ofpieces of data is not 0. If the packetizing unit 22 determines that thenumber #1 of pieces of data is not 0 (No in S202), it reads the packetWP from the storage unit 18 (S204), increments a read count RC by 1, andoutputs the packet WP to the transmitting unit 26. The read count RCindicates the number of operations of reading data from the storage unit18, performed for one packet WP. The packetizing unit 22 determineswhether the read count RC is equal to the fixed length WL of the packetWP (S206). The packetizing unit 22 repeats steps S202 to S206 (No inS206) until the read count RC becomes the fixed length WL. It is notedthat, in step S202 performed after step S206, the number #1 of pieces ofdata can be determined to be 0.

In the case where the packetizing unit 22 determines that the read countRC has become the fixed length WL (Yes in S206), it determines whetherthe number #1 of pieces of data is greater than N which is the number ofpieces of data for determination (S208). The number N for determinationis a value used for optimizing the latency. The smaller value is morepreferable; the ideal value is 0. In the case where the number N fordetermination is 0, the data left in the storage unit 18 is zero in thestate where the packet WP has been read from the storage unit 18.

If the packetizing unit 22 determines that the number #1 of pieces ofdata is greater than the number N for determination (Yes in S208), itresets the threshold value Th to “Th−(#1−N)” (S210). In this manner, thepacketizing unit 22 reduces the threshold value Th. On the other hand,if the packetizing unit 22 determines that the number #1 of pieces ofdata is not greater than the number N for determination (No in S208), itdoes not reset the threshold value Th. Thereafter, the packetizing unit22 initializes the read count RC (S212), and repeats step S200 andsubsequent steps.

In the case where the packetizing unit 22 determines in step S202 thatthe number #1 of pieces of data is 0 (Yes in S202), it means an errorstate in which no data is left in the storage unit 18, i.e. shortage ofdata. Therefore, the packetizing unit 22 resets the threshold value Thto “Th+(WL−RC)” so as to reduce the shortage of data (S218). In otherwords, the packetizing unit 22 adjusts the threshold value Th on thebasis of the read count RC that indicates the amount of data read fromthe storage unit 18. In this manner, the packetizing unit 22 slightlyincreases the too small threshold value Th, which can suppress shortageof the data stored in the storage unit 18. Thereafter, the packetizingunit 22 adds the null data IFS to the packet WP (S220), without readingthe data in the storage unit 18, while incrementing the read count RC.Thereafter, the packetizing unit 22 repeats step S220 (No in S222) untilthe read count RC becomes the fixed length WL. Once the packetizing unit22 determines that the read count RC has become the fixed length WL (Yesin S222), it resets the region corresponding to the packet in thestorage unit 18 (S226), and repeats step S200 and subsequent steps.

FIG. 8 is a flowchart illustrating a process of writing a receivedfixed-length packet WP to the storage unit 18, performed by the datagenerating unit 32 in the receiving device 16. As shown in FIG. 8, inthe writing process in the receiving device 16, the data generating unit32 determines whether data in the form of radio carrier wave has beenreceived (S300). The data generating unit 32 repeats step S300 (No inS300) until the data in the form of radio carrier wave is received. Ifthe data generating unit 32 determines that the data in the form ofradio carrier wave has been received (Yes in S300), it determineswhether the received data is the head of a packet WP (S302). If the datagenerating unit 32 determines that it is not the head of the packet WP(No in S302), it determines whether the received data is null data IFS(S304). If the data generating unit 32 determines that the received datais not null data IFS (No in S304), it means that the received data isactual data PC. In this case, the data generating unit 32 writes thedata, which is the actual data PC, into the storage unit 18 (S306), andthen repeats step S300 and subsequent steps.

On the other hand, if the data generating unit 32 determines that thereceived data is null data IFS (Yes in S304), it determines whether adelete count RV is greater than 0 (S308). The delete count RV, which isa value for determining whether to delete null data IFS or not, isdecremented by 1 every time the null data IFS is deleted. If the datagenerating unit 32 determines that the delete count RV is greater than 0(Yes in S308), the data generating unit 32 determines whether the nulldata amount IT, corresponding to the time during which null data IFScontinues after actual data PC, is greater than a minimum amount MinITof the null data amount IT (S310). The minimum amount MinIT is 96 bits,for example. If the data generating unit 32 determines that the nulldata amount IT is greater than the minimum amount MinIT (Yes in S310),it decrements the delete count RV by 1, and deletes the received nulldata IFS (S312). In this manner, the data generating unit 32 can adjustthe clock timing, by deleting the null data IFS, so as to comply withthe Ethernet standard. Thereafter, the data generating unit 32 repeatsstep S300 and subsequent steps. On the other hand, if the datagenerating unit 32 determines that the delete count RV is 0 or less (Noin S308) or determines that the null data amount IT is equal to or lessthan the minimum amount MinIT (No in S310), then the data generatingunit 32 writes the received null data IFS, as data, into the storageunit 18 (S306).

When the data generating unit 32 determines in step S302 that thereceived data in the form of radio carrier wave is the head of a packetWP (Yes in S302), it determines whether the number #2 of pieces of data,indicating the number of pieces of data remaining in the storage unit18, is greater than a threshold value Tha (S320). The threshold valueTha is a predetermined value used for determining whether to write newlyreceived null data IFS into the storage unit 18 or delete it. In otherwords, the threshold value Tha is the ideal number of pieces of data ofthe preceding packet WP being left in the storage unit 18 at the timewhen a new packet WP is received. The ideal threshold value Tha is avalue that can improve the latency and eliminate shortage of data. As anexample, the threshold value Tha can be two to four. If the datagenerating unit 32 determines that the number #2 of pieces of data isgreater than the threshold value Tha (Yes in S320), it means that thenumber #2 of pieces of data remaining in the storage unit 18 is toolarge. Therefore, the data generating unit 32 resets the delete count RVto “#2−Tha” (S322) such that the number #2 of pieces of data remainingat the time of arrival of the head of the packet WP is decreased andthat the shortage of data is prevented. Thereafter, the data generatingunit 32 deletes the null data IFS in step S312. In this manner, the datagenerating unit 32 is able to delete the null data IFS until the deletecount RV becomes 0, to thereby reduce the number #2 of pieces of data atthe time when a new packet WP is received and, thus, to improve thelatency. For example, in the case where the Ethernet clock on thetransmitting side is faster than the Ethernet clock on the receivingside, the number #2 of pieces of data remaining in the storage unit 18can become too large. On the other hand, if the data generating unit 32determines that the number #2 of pieces of data is not greater than thethreshold value Tha (No in S320), it means that the number #2 of piecesof data left is appropriate, and therefore, the data generating unit 32does not reset the delete count RV. Thereafter, the data generating unit32 performs step S304 and subsequent steps. In this manner, the datagenerating unit 32 is able to perform cycle adjustment in the receivingdevice 16, on the basis of the number #2 of pieces of data in thestorage unit 18 at the time of arrival of the head of the packet WP, or,on the basis of the remaining amount of data.

FIG. 9 is a flowchart illustrating a process of reading a fixed-lengthpacket WP written in the storage unit 18, performed by the datagenerating unit 32 in the receiving device 16. As shown in FIG. 9, inthe reading process in the receiving device 16, the data generating unit32 determines whether the number #2 of pieces of data in the storageunit 18 is 0 (S400). If the data generating unit 32 determines that thenumber #2 of pieces of data is not 0 (No in S400), it determines whetherthe number #2 of pieces of data is greater than a threshold value Thb(S402). The threshold value Thb is a value for determining whether toadd null data IFS or not. If the data generating unit 32 determines thatthe number #2 of pieces of data is greater than the threshold value Thb(Yes in S402), it reads the continuous data SD including the Ethernetactual data PC and the null data IFS, stored in the storage unit 18(S404), and outputs the read data to the data transmitting unit 34.

When the data generating unit 32 determines in step S402 that the number#2 of pieces of data is not greater than the threshold value Thb (No inS402), it determines whether the immediately preceding data was actualdata PC (S406). If the data generating unit 32 determines that theimmediately preceding data was actual data PC (Yes in S406), it performsstep S404. On the other hand, if the data generating unit 32 determinesthat the immediately preceding data was not actual data PC (No in S406),i.e. if the immediately preceding data was null data IFS, the datagenerating unit 32 adds the null data IFS (S408), and repeats step S400and subsequent steps, without reading the continuous data SD in thestorage unit 18. In this manner, even in the case where the number #2 ofpieces of data is smaller than the threshold value Thb, the datagenerating unit 32 can add null data IFS following the preceding nulldata IFS, to secure the number of pieces of data that can resolveuncertainty in the receiving time in the storage unit 18 and to suppressshortage of the data stored in the storage unit 18. If the datagenerating unit 32 determines in step S400 that the number #2 of piecesof data is 0 (Yes in S400), i.e. if no data is remaining in the storageunit 18, the data generating unit 32 determines whether the immediatelypreceding data was actual data PC (S410). If the data generating unit 32determines that the immediately preceding data was not actual data PC(No in S410), it performs step S408 and subsequent steps. On the otherhand, if the data generating unit 32 determines that the immediatelypreceding data was actual data PC (Yes in S410), it adds null data IFSfor error handling (S412). Thereafter, the data generating unit 32resets the threshold value Thb to “Thb+1” (S414), and repeats step S400and subsequent steps.

As described above, in the communication system 10, the control unit 24in the transmitting device 14 reduces the radio carrier wave transmittedby the transmitting unit 26. This can reduce the operating cost and alsodecrease the consumed power. Further, as the transmission of radiocarrier wave is reduced in the communication system 10, even if thenumber of the communication devices 12 increases, the interference andcrosstalk between the radio carrier waves transmitted by the respectivecommunication devices 12 can be reduced. Therefore, the communicationdevices 12 can implement spatial multiplexing of wireless channels evenin the 60 GHz band with only four channels, for example.

Furthermore, in the communication system 10, the packetizing unit 22deletes at least a part of the null data IFS. This can reduce the timeinterval between the pieces of actual data PC. The latency in thecommunication system 10 can therefore be improved.

A description will be made below of simulations for proving theabove-described effects. FIG. 10 is a graph showing the relationshipbetween the percentage of null data IFS and the percentage of reductionin output. The percentage of reduction in output was measured for threedifferent wireless communication speeds. The size of packet WP was 4096bytes. The simulation conditions in FIG. 10 were as follows:

(Condition 1) Communication speed of Ethernet: 1 Gbps

(Condition 2) [Operating power (for receiving radio carrier waves) ofthe transmitting unit 26 and the receiving unit 30]:[Power consumed bythe always-on circuits in the communication device 12 other than thetransmitting unit 26 and the receiving unit 30]=1:1(Condition 3) [Standby power of the transmitting unit 26 and thereceiving unit 30]:[Operating power (for receiving radio carrier waves)of the transmitting unit 26 and the receiving unit 30]=1:2

It is apparent from FIG. 10 that the percentage of reduction in outputincreases with the increase of the percentage of null data IFS. It isalso apparent that, with the same percentage of null data IFS, thepercentage of reduction in output increases with the increase of thecommunication speed. It is therefore understood that the communicationsystem 10 described above can reduce the power consumption particularlyin the case where the communication speed is fast and the percentage ofnull data IFS is large. For example, the communication system 10 canreduce the power consumption by 15% to 30% under the above-describedconditions.

FIG. 11 is a graph showing the relationship between the size of packetWP and the percentage of reduction in output. The percentage ofreduction in output was measured for three different wirelesscommunication speeds. The percentage of null data IFS was 80%. Thesimulation conditions in FIG. 11 were identical to the conditions 1 to 3in FIG. 10.

It is apparent from FIG. 11 that the percentage of reduction in outputincreases with the increase of the size of packet WP. It is alsoapparent that, with the same size of packet WP, the percentage ofreduction in output increases with the increase of the communicationspeed. It is further apparent that the reduction in output accompanyingthe increase in size of packet WP is particularly noticeable when thecommunication speed is fast.

FIG. 12 is a graph showing the relationship between the size of packetWP and the latency. The latency was measured for a variable-lengthpacket WP and for three different communication speeds for afixed-length packet WP. In FIG. 12, the Ethernet communication speed was1 Gbps.

It is apparent from FIG. 12 that the latency improves with the reductionin size of the packet WP. It is also apparent that the latency improvesin the case of transmitting/receiving fixed-length packets WP generatedby dividing Ethernet actual data PC, as compared with the case oftransmitting/receiving variable-length packets WP which are generated inunits of Ethernet actual data PC. For example, it is apparent that, forsome wireless communication speed and some size of packet WP, thelatency in the case of transmitting/receiving fixed-length packets canbe made about one-eighths of the latency in the case oftransmitting/receiving variable-length packets.

The arrangement of the constituent elements, their connectionrelationship, and the numerical values such as the number of pieces, thenumber of bits, etc. in the above-described embodiment can be changed asappropriate. Further, different embodiments can be combined.

For example, in the above-described embodiment, the mode of transmittinga variable-length packet WP and the mode of transmitting a fixed-lengthpacket WP were described independently from each other. Alternatively,the transmitting unit 26 can switch between a fixed-length packet WPwhose data amount is predetermined, and a variable-length packet WPwhose data amount can vary, for transmission. In this case, it ispreferable for the transmitting unit 26 to transmit a fixed-lengthpacket WP in the case where the spacing between the pieces of Ethernetactual data PC is less than a spacing threshold value. Further, it ispreferable for the transmitting unit 26 to transmit a variable-lengthpacket WP in the case where the spacing between the pieces of Ethernetactual data PC is not smaller than the spacing threshold value. It isalso preferable for the packetizing unit 22 to generate avariable-length packet WP, with all null data IFS deleted, in the casewhere the spacing between the pieces of Ethernet actual data PC is notsmaller than the spacing threshold value. Further, it can be configuredsuch that the constituent elements in the above-described embodimentfunction as a computer reads a program for transmission or a program forreception.

FIG. 13 shows, by way of example, the hardware configuration of acomputer 1900 according to the present embodiment. The computer 1900according to the present embodiment is an example of an informationprocessing unit. The computer 1900 includes: a CPU peripheral portionhaving a CPU 2000 and a RAM 2020 connected to each other via a hostcontroller 2082; an input/output portion having a communicationinterface 2030 and a hard disk drive 2040 connected to the hostcontroller 2082 via an input/output controller 2084; and a legacyinput/output portion having a ROM 2010, a memory drive 2050, and aninput/output chip 2070 connected to the input/output controller 2084.

The host controller 2082 connects the RAM 2020 with the CPU 2000 whichaccesses the RAM 2020 at a high transfer rate. The CPU 2000 operates onthe basis of the programs stored in the ROM 2010 and the RAM 2020 forcontrol of the respective portions. The input/output controller 2084connects the host controller 2082 with the communication interface 2030and the hard disk drive 2040, which are relatively fast input/outputdevices. The communication interface 2030 communicates with otherapparatuses via a network. The hard disk drive 2040 stores a displayprogram and other programs and data used by the CPU 2000 in the computer1900.

Further, the input/output controller 2084 is connected with the ROM 2010and the relatively slow input/output devices of the memory drive 2050and the input/output chip 2070. The ROM 2010 stores a boot programexecuted at the time of activation of the computer 1900 and/or a programdependent on the hardware of the computer 1900. The memory drive 2050reads a program, such as a display program, or data from a memory card2090, and provides the program or data to the hard disk drive 2040 viathe RAM 2020. The input/output chip 2070 connects the memory drive 2050to the input/output controller 2084, and also connects variousinput/output devices to the input/output controller 2084 via, e.g., aparallel port, serial port, keyboard port, or mouse port.

The program to be provided to the hard disk drive 2040 via the RAM 2020is stored in a recording medium, such as the memory card 2090 or an ICcard, and is provided by a user. The program such as a display programis read from the recording medium and installed via the RAM 2020 to thehard disk drive 2040 in the computer 1900, for execution in the CPU2000.

The program for transmission, installed into the computer 1900 forcausing the computer 1900 to function as the communication device 12includes: a data receiving module, a packetizing module, a controlmodule, and a transmitting module. These programs or modules work on theCPU 2000 and the like to cause the computer 1900 to function as: thedata receiving unit 20, the packetizing unit 22, the control unit 24,and the transmitting unit 26, respectively.

The information processing described in these programs is read into thecomputer 1900 to function as the data receiving unit 20, the packetizingunit 22, the control unit 24, and the transmitting unit 26, which arethe specific means realized by cooperation of the software and thehardware resources described above. These specific means implementinformation computation or processing, in accordance with the intendeduse of the computer 1900 of the present embodiment, to thereby establishthe communication device 12 dedicated to the intended use.

The program for reception, installed into the computer 1900 for causingthe computer 1900 to function as the communication device 12 includes: areceiving module, a data generating module, and a data transmittingmodule. These programs or modules work on the CPU 2000 and the like tocause the computer 1900 to function as: the receiving unit 30, the datagenerating unit 32, and the data transmitting unit 34, respectively.

The information processing described in these programs is read into thecomputer 1900 to function as the receiving unit 30, the data generatingunit 32, and the data transmitting unit 34, which are the specific meansrealized by cooperation of the software and the hardware resourcesdescribed above. These specific means implement information computationor processing, in accordance with the intended use of the computer 1900of the present embodiment, to thereby establish the communication device12 dedicated to the intended use.

For example, in the case where the computer 1900 communicates with anexternal device or the like, the CPU 2000 executes a communicationprogram loaded onto the RAM 2020 and, on the basis of the content ofprocessing described in the communication program, instructs thecommunication interface 2030 to perform the communication processing.The communication interface 2030, under the control of the CPU 2000,reads send data, stored in a transmission buffer area provided on astorage device such as the RAM 2020, hard disk drive 2040, or memorycard 2090, and transmits the obtained send data to the network, orreceives data from the network and writes the received data into areception buffer area provided on a storage device. In this manner, thecommunication interface 2030 can transfer send/receive data to and froma storage device using the direct memory access (DMA) system.Alternatively, the CPU 2000 can read data from a source storage deviceor the communication interface 2030 and write the data to a destinationcommunication interface 2030 or storage device, for transferring thesend/receive data.

Further, the CPU 2000 reads a whole or necessary part of the files ordatabases stored in an external storage device such as the hard diskdrive 2040 or memory drive 2050 (memory card 2090) into the RAM 2020 viaDMA transfer or the like, and performs various processing on the data onthe RAM 2020. The CPU 2000 then writes the processed data back to theexternal storage device via DMA transfer or the like. During theprocessing, the RAM 2020 temporarily stores the content of the externalstorage device. Thus, in the present embodiment, the RAM 2020 and theexternal storage devices are collectively referred to as the memory,storage unit, or storage device. Various information including variousprograms, data, tables, and databases in the present embodiment isstored in such storage devices and subjected to information processing.It is noted that the CPU 2000 can store a part of the content in the RAM2020 in a cache memory for reading/writing data on the cache memory. Insuch an embodiment as well, the cache memory performs a part of thefunction of the RAM 2020. Therefore, in the present embodiment, it isassumed that the cache memory is also included in the RAM 2020, memory,and/or storage device, unless otherwise specified.

The CPU 2000 performs various processing on the data read out of the RAM2020. The processing can include various computation, informationprocessing, conditional judgment, and information search andreplacement, described in the present embodiment, which are designatedby sequences of instructions in programs. The CPU 2000 then writes theprocessed data back to the RAM 2020. For example, in the case ofperforming the conditional judgment, the CPU 2000 determines whethervarious variables described in the present embodiment each satisfy acondition that it is greater than, smaller than, not smaller than, notgreater than, or equal to another variable or constant, and if thecondition is satisfied (or not satisfied), branches to a differentsequence of instructions, or calls a sub-routine. The CPU 2000 can alsosearch the information stored in the databases or the files within thestorage device.

The programs or modules described above can be stored in an externalrecording medium. The recording medium can be, besides the memory card2090, an optical recording medium such as a DVD or a CD, amagneto-optical recording medium such as an MO, a tape medium, or asemiconductor memory such as an IC card. Further, a storage device suchas a hard disk or a RAM provided in a server system connected to aprivate communication network or the Internet can be used as a recordingmedium, and the program can be provided to the computer 1900 via thenetwork.

While the present invention has been described above with reference tothe embodiment, the technical scope of the present invention is notlimited to that of the above-described embodiment. It is apparent tothose skilled in the art that various modifications or improvements arepossible for the above-described embodiment. It is evident fromdescription of the claims that the embodiments modified or improved arealso within the technical scope of the present invention.

It should be noted that the operations, procedures, steps, or stages ofeach process performed by the device, system, program, or method shownin the claims, specification, or diagrams can be performed in any orderunless the order is explicitly indicated by “before”, “prior to” or thelike or unless the output from a previous process is used in a laterprocess. Even if the process flow is described using phrases such as“first”, “next” or the like for convenience′ sake in the claims,specification, or diagrams, it does not necessarily mean that theprocess must be performed in the described order.

The invention claimed is:
 1. A transmission method comprising: a datareceiving step of receiving continuous data from a network, thecontinuous data including actual data and null data; a packetizing stepof deleting at least a part of the null data from the continuous data togenerate a packet for wireless communication; a transmitting step ofmodulating the packet into a radio carrier wave and wirelesslytransmitting the resulting packet, wherein the transmitting stepswitches between a packet of fixed length with a predetermined dataamount, and a packet of variable length with a variable data amount; anda control step of causing transmission of the radio carrier wave in thetransmitting step to be stopped during at least a part of a time periodin which no such packet is transmitted wirelessly.
 2. The transmissionmethod of claim 1, wherein the packetizing step adds null data to thehead of a next packet when the packet of fixed length has a tail endthat coincides with a tail end of the actual data in the continuousdata.
 3. The transmission method of claim 1, wherein the transmittingstep begins only after the continuous data has been processed by apredetermined data amount or more and stored in the storage unit, andwherein the packetizing step stores the packet of the predeterminedfixed length, and adjusts a threshold value used for determining whetherthe packet can be read from the storage unit or not, on the basis of theamount of data read from the storage unit.
 4. A receiving methodcomprising: a receiving step of demodulating a radio carrier wavetransmitted wirelessly from a transmitting side into a packet andreceiving a resulting packet, the radio carrier wave being transmittedin a state where at least a part of null data has been deleted on thetransmitting side from continuous data received from a first network,the continuous data including actual data and the null data; a storingstep of storing at least one piece of data in a packet of fixed length;a data generating step of adding the null data to, or deleting the nulldata from, the packet to generate continuous data, wherein the datagenerating step further comprises: determining that data in a form ofthe radio carrier wave is received; determining that the data in theform of the radio carrier wave is a head of the packet; determining thata number of pieces of data remaining in a storage unit is greater than afirst threshold value; resetting a delete count; deleting the null datauntil the delete count is 0; and writing the data in the form of theradio carrier wave to the storage unit; and a data transmitting step oftransmitting the continuous data including the actual data and the nulldata to a second network.